1. Technical Field
The present disclosure relates to methods for making electrode material applied in a lithium-ion battery, and particularly to a method for making a lithium titanate composite electrode material.
2. Description of Related Art
Lithium titanate (Li4Ti5O12) with spinel structure is a novel electrode material used in energy storage batteries and has received a great deal of interest recently. Lattice parameters of the lithium titanate have extremely small variations when lithium-ions are cycled in and out during a charging and discharging process of the battery. Thus, the lithium titanate has been reported as a “zero strain” electrode material, and has an excellent cycling property. Electrodes made of lithium titanate can undergo many hundreds of cycles without structural disintegration, thereby increasing the lifespan of the batteries, and decreasing an attenuating speed of the specific capacity of the electrodes. However, lithium titanate has lower conductivity, charge and discharge rate, and tap density than other electrode materials such as lithium manganate.
Presently, different methods are used for solving the above problems including: fabricating nanoscale lithium titanate to shorten diffusion paths of lithium ions and increase surface area for electrochemical reaction; mixing conductive carbon particles with the lithium titanate powder, or doping metal ions into the lithium titanate powder. A method for making a lithium titanium composite material is known. In the method, a solid phase lithium salt, a solid phase titanium dioxide (TiO2), and a dispersing agent are mixed according to a certain proportion. The mixture is then ball milled to form a precursor. A number of lithium titanate particles are fabricated by heating the precursor for a period of time. Furthermore, the lithium titanate particles are coated by carbon source by using an immersion method, and then the carbon source is pyrolyzed to form a carbon layer coated on each of the lithium titanate particles. The conductivity and the discharge rate of the lithium titanate composite material are improved by the addition of the carbon layer.
However, the above precursor is formed by using a solid phase mixing method. The lithium salt and the solid phase titanium dioxide are simply mixed together. As a result, the lithium titanate particles are irregularly shaped and vary in diameter. Thus, the carbon source coated on the surfaces of each of the lithium titanate particles is easily segregated and crystallized during pyrolyzing. Accordingly, a carbon layer, formed by pyrolyzing the carbon source, may non-uniformly coat the surfaces of each of the lithium titanate particles, thereby decreasing electrochemical property of the electrode material of lithium-ion battery.
What is needed, therefore, is to provide a method for making a lithium titanate composite electrode material having a uniform carbon layer coating the surfaces of each of the lithium titanate particles.